Regulation of gene expression in animal cells is of central importance to development, the action of many hormones, and homeostasis in the adult. Abnormal patterns of regulation underly many human clinical conditions. This proposal focuses on a prominent, but relatively neglected aspect of gene regulation in animal cells - post-transcriptional regulation. A simian tumor virus, SV40, is used as a model. Unlike bacterial mRNA, eukaryotic mRNA is formed by extensive modification of a primary transcript. In principle, each mRNA maturation step provides a means of regulating mRNA formation. This proposal focuses on the molecular basis of two of these steps: the cleavage reaction which forms the 3' terminus of mRNA from a longer precursor, and its polyadenylation. The experiments are designed to shed lights on the relationship between these steps and the transport of mRNA from nucleus to cytoplasm. The approach taken is very similar to that which has lead to impressive progress in understanding transcriptional regulation in both prokaryotes and eukaryotes. The central strategy involves the generation and use of a battery of mutations constructed in a small region of SV40 DNA which is sufficient to direct cleavage, polyadenylation, and transport. The ability of these mutant templates to direct accurate processing will be assayed in vivo, both injection into frog oocytes and transformation of cultured monkey cells. Three main points are addressed. 1. What minimum sequences are necessary and sufficient for cleavage, polyadenylation, and transport of an mRNA precursor? 2. Do processing steps form an obligatory mRNA maturation pathway, or can they be uncoupled? 3. What factors recognize mRNA precursors and modify them through these three steps?